长江三角洲及邻近海域第一硬质黏土层的生物化石标志

FOSSIL SIGN IN THE UPPERMOST HARD CLAY OF THE YANGTZE DELTA AND ADJACENT CONTINENTAL SHELVES

对长江三角洲地区8个钻孔进行了系统的孢粉、藻类分析,从第一硬质黏土层中提取出较丰富的孢粉和藻类化石,结合其他学者的研究成果,探讨了长江三角洲及邻近海域第一硬质黏土层中的孢粉、藻类及其组合的特征。与其上覆地层相比,硬质黏土层中的孢粉、藻类的绝对浓度较低,出现的孢粉、藻类组合较单调,孢粉、藻类组合中淡水藻类含量异常高,并以环纹藻为主。高含量的淡水藻类指示硬质黏土的形成曾受到水流作用,硬质黏土的形成环境应为水域环境。与上覆、下伏地层的孢粉、藻类组合明显不同,淡水藻类含量高是第一硬质黏土层孢粉、藻类组合的重要特征,可以作为长江三角洲及其邻近海域地区晚第四纪地层对比的一个显著标志。

Systemic palynomorphs analysis from 8 cores in the Yangtze Delta was made and relatively abundant palynomorphs have been recovered from the late Pleistocene uppermost hard clay. Combined research results of other researchers, palynomorphs and palynomorphs assemblages characteristics of the uppermost hard clays in the Yangtze Delta and adjacent continental shelves were discussed. Palynomorphs concentrations in the uppermost hard clay were relatively low. Palynological assemblages were relatively humdrum, while the content of freshwater alga was unconventionally high in the uppermost hard clay. High content of freshwater alga shows that the formation of the hard clays was influenced by water and the hard clays should be freshwater deposits. Palynomorphs assemblages in the hard clays were obviously different from those in the overlaying and underlying layers. High percentage of freshwater algae is the most remarkable characteristic of the palynomorphs assemblage of the Yangtze Delta. High percentage of freshwater algae is the fossil sign of the uppermost hard clay of the Yangtze Delta and adjacent continental shelves.